Technical Field
The present invention relates to an optical fiber and a process for producing the optical fiber.
Background Art
Japanese Patent No. 4341872 describes a radiation-curable liquid resin composition for the inner primary coating of optical fibers, the composition containing an oligomer which has a reactive group at each of both ends.
Optical fibers are required to have resistance to lateral pressure. The resistance to lateral pressure is unsusceptibility to the transmission loss induced by micro-bending which occurs when lateral pressure is applied to the optical fiber. In order for an optical fiber to have resistance to lateral pressure, the inner coating layer needs to decrease its Young's modulus. According to the technique described in the patent document, it is necessary that the molecular weight of the oligomer should be increased for decreasing the Young's modulus of the primary coating of the optical fiber. In this case, however, toughness of the primary coating has been decreased to pose a problem in that polymer chains in the resin undergo irreversible breakage due to tension and accumulation thereof results in void generation. The presence of voids enhances low-temperature transmission loss.